In order to measure certain physical properties, such as density, moisture content and compressive strength of some materials such as soil or paving material, loose samples of the soil or paving material are formed into test specimens under reproducible conditions using laboratory compaction machines. In order to replicate actual expected conditions, it is desirable to compact the test specimens under conditions that simulate actual use. For a paving material sample, this requires simulation of the kneading force applied to the paving material by a paving roller, such as rollers with smooth or sheeps/pad-foot drums or pneumatic wheels, or vibratory compactors such as those used in intelligent compaction. Simply applying a compressive force to the sample does not adequately simulate the kneading action of the paving roller, as the paving roller also applies a shear force to the material being compacted. As a result, compaction machines that apply an orbital motion to the paving sample during compression have been developed to simulate actual conditions of use. For simplicity of implementation and analysis, the orbital motion in many current compaction machines has been restricted to gyration along a circular orbit.
The combination of shear and compaction effort applied to the gyrating specimen is designed to mimic the kneading effect of in-situ compaction of a material using a rolling compactor. Typically, the gyration of the mold is performed with an offset so that the axis of the mold is at an angle from the compression force from the ram. The corresponding average angle between the direction of the compression force and the position of the mold axis is often referred to as the internal angle.
This internal angle is the angle of applied confinement forces with respect to the main axis of rotation that the specimen is really subject to. Its measurement and calibration is typically performed using a self-contained device such as the Rapid Internal Angle Measurement (RAM) unit, an example of which is disclosed in U.S. Pat. No. 6,925,889, or Dynamic Angle Validator (DAV), an example of which is disclosed in U.S. Pat. No. 6,477,783B1. These devices are shear force simulation devices that mimic the shear effort applied to a material and have the capability to also measure, store, and display the internal angle by way of difference of distance measurement of the position of the inside of the mold with respect to the perpendicular direction to a mold plate. A simple way to infer the internal angle applied to the sample material is to measure the external angle, i.e., the angle between the reference frame and the mold. However, when forces are applied to the frame and the mold, the frame can flex, the ram position and direction of force can vary, and the corresponding perpendicular direction of the mold plates can change with respect to the inside axis of the mold. These are not the exhaustive list of factors that can affect the actual internal angle versus the measured internal angle. They are, however, the main variables that can make the relationship between internal angle and external angle vary in time between the top and bottom of the sample.
Various disadvantages have been associated with previously developed gyratory compactors. For example, some gyratory compactors include a ram applying compressive force from one end of a cylindrical mold, while the other end of the mold is gyrated by rotating a base supporting the other end of the mold. However, these machines could not easily determine and maintain a consistent angle of gyration due to inconsistencies during rotation of the base supporting the other end of the mold and flexure of the gyratory compactor during operation. Most implementations included the use of a mechanical interference to constrain the shape of the gyration motion.
Another example of a gyratory compactor apparatus is disclosed in U.S. Pat. No. 5,939,642 to King et al. (the '642 patent). The '642 patent describes a gyratory compactor apparatus design for facilitating ergonomics and efficiency, while improving consistency of operating parameters. The gyratory compactor described therein allows the user to slide the cylindrical compaction mold into the compaction chamber without the necessity of lifting the mold. In addition, the compactor of the '642 patent includes an integral specimen removal ram, which facilitates easy removal of the specimen from the mold. In addition, the frame design reduces frame deflection that could undesirably affect the angle of gyration. Further, the angle of gyration of the compactor apparatus can be changed by simply replacing a single component of the apparatus. Notwithstanding the advances that have been made in the art of gyratory compactors, there is a need for smaller and less costly designs, with improved operational efficiency and accuracy. Additionally, there is a need for a gyratory compactor having improved ergonomics. For example, placement and removal of the mold containing the sample should be accomplished with minimal difficulty. Additionally, it would be desirable to produce a lightweight frame design that also minimizes frame flexure, thus providing more accurate test results. Moreover, it would be advantageous to enable release of water content when the sample material is fully or partially saturated soil or emulsified asphalt. Also, it would be advantageous to provide a compactor design that allows the user to quickly, easily, dynamically, and/or in real-time change, control, and calibrate operating parameters, such as the angle of gyration, shape of gyration, and ability to control applied axial load. Further, there is a need in the art for a gyratory compactor that provides a constant, precise, and accurate internal angle of gyration during the compaction procedure with minimal deviation therefrom.